1. Field of the Invention
This invention relates generally to a process for removing methanol from an alkylation unit feed stream, and more particularly, to a process for removing methanol from the hydrocarbon phase produced in the fractionation of an MTBE reaction mixture whereby the hydrocarbon phase can be utilized as an alkylation unit feed.
2. Description of the Prior Art
In producing gasoline it has become desirable to utilize high octane blending components such as methyl tertiary butyl ether (MTBE) so that blends of unleaded gasoline can be of the required octane rating. MTBE is typically produced in a process wherein methanol is catalytically reacted with isobutene in a mixed C.sub.4 hydrocarbon stream. The mixed C.sub.4 hydrocarbon stream is commonly derived from conventional fluid catalytic cracking units and coking operations present in crude oil refineries.
In the MTBE production process, a stochiometric excess of methanol is mixed with the isobutene present in the mixed C.sub.4 hydrocarbon stream in the presence of an acidic ion exchange catalyst such as AMBERLYST-15. AMBERLYST-15 is commercially available from the Rohm & Haas Company of Philadelphia, Pa. and is a cationic, strongly acidic, ion exchange resin containing a sulfonated polystyrene crosslinked with divinylbenzene. The excess of methanol is used to obtain a good conversion of isobutene and to suppress side reactions resulting in low octane polymers.
The catalytic alkylation of isobutane with olefins such as butenes is also a well known process utilized in refineries for producing high octane gasoline components. Generally, refinery alkylation units utilize a stream of acid as the catalyst and produce a spent acid stream.
While the unreacted C.sub.4 hydrocarbon stream remaining after separation of produced MTBE therefrom has heretofore been charged to an alkylation unit as a feed stream thereto, because of the presence of methanol in the stream it has been necessary to subject the stream to a methanol removal process. That is, the presence of methanol in the alkylation unit hydrocarbon feed stream from the MTBE production process is detrimental to the alkylation unit since methanol reacts with isobutane and acid to produce undesired low octane compounds and catalyst diluting water.
The methanol removal processes heretofore utilized include adsorption and absorption processes. For example, U.S. Pat. No. 4,490,563 issued Dec. 25, 1984, describes a system which includes the water absorption of methanol to remove it from the unreacted C.sub.4 effluent produced in an MTBE production and separation process. Such methanol removal processes have been used successfully, but they generally require relatively elaborate equipment and are expensive to carry out.
Thus, there is a need for a simple and inexpensive process for removing methanol from the MTBE production process unreacted hydrocarbon effluent prior to charging such effluent to an alkylation unit.